AMH in blood is a marker of ovarian status in women and the presence of cryptic testes in babies. Despite this, the molecular form of AMH in blood has not been verified. AMH is synthesized as an inert proprotein precursor (proAMH), which can be cleaved to yield N-terminal (AMH_N), and C-terminal (AMH_C) fragments, that can complex non-covalently (AMH_N,C). Developing males have tenfold more AMH than young adults. We report here, that human blood is a mixture of inactive proAMH and receptor-binding AMH_N,C. The AMH in the blood of boys, men and premenopausal women was immunoprecipitated using antibodies to the N- and C-terminal peptides. The precipitated proteins were then analyzed by western blots, using recombinant proteins as markers. The glycosylation status of AMH was verified using deglycosylating enzymes. The N-terminal antibody precipitated a major protein that migrated alongside rhproAMH and was detected by anti-AMH_N and anti-AMH_C. This antibody also precipitated significant levels of AMH_N and AMH_C from all participants. Antibodies specific to AMH_C precipitated rhAMH_C, but did not precipitate AMH_C from human blood. Hence, all the AMH_C in human blood appears to be bound to AMH_N. Both AMH_N and proAMH were glycosylated, independent of age and sex. In conclusion, boys and young adults have the same form of AMH, with a significant proportion being the inactive precursor. This raises the possibility that the endocrine functions of AMH are partly controlled by its cleavage in the target organ. The presence of proAMH in blood may confound the use of AMH for diagnosis.